watchdog.py

A lightweight, cross-platform process watchdog. No third-party dependencies.

Checks if a target process is running every minute via cron/schtasks, and starts it if not.

Features

• ✅ Cross-platform: Windows & Linux
• ✅ No third-party dependencies (stdlib only)
• ✅ Multi-task support via JSON config
• ✅ Process matching by cmdline substring (not just process name)
• ✅ PID file to prevent concurrent watchdog instances
• ✅ No console window flicker on Windows (pythonw.exe)

Quick Start

1. Config file (recommended, supports multiple tasks)

Create watchdog.json in the same directory as watchdog.py:

{
    "tasks": [
        {
            "cmd":   "ssh -N -D 10081 root@myhost -p 2222 -o ServerAliveInterval=30 -o ServerAliveCountMax=3",
            "match": "-D 10081",
            "log":   "/var/log/ssh-watchdog.log"
        },
        {
            "cmd":   "frpc -c /etc/frpc.ini",
            "match": "frpc.ini"
        }
    ]
}

Then run:

python watchdog.py

log is optional — defaults to watchdog.log in the same directory.

2. Command line (single task)

python watchdog.py --cmd "ssh -N -D 10081 root@myhost" --match "-D 10081"

Priority: CLI args > config file > defaults.

Scheduling

Windows (schtasks)

Run in PowerShell — no console window flicker:

# Register (every minute)
schtasks /create /tn "Watchdog" /tr '"C:\path\to\pythonw.exe" "C:\path\to\watchdog.py"' /sc minute /mo 1 /ru $env:USERNAME /f

# Run immediately
schtasks /run /tn "Watchdog"

# Query
schtasks /query /tn "Watchdog" /fo list

# Change interval (e.g. every 5 minutes)
schtasks /change /tn "Watchdog" /sc minute /mo 5

# Disable / Enable
schtasks /change /tn "Watchdog" /disable
schtasks /change /tn "Watchdog" /enable

# Delete
schtasks /delete /tn "Watchdog" /f

Use pythonw.exe (same directory as python.exe) to avoid console window flicker.

Linux (crontab)

crontab -e

Add:

* * * * * python3 /path/to/watchdog.py

Log Output

2026-05-06 10:00:01 [OK]   '-D 10081' already running (PID: 4321)
2026-05-06 10:01:01 [WARN] '-D 10081' not found, starting: ssh -N -D 10081 ...
2026-05-06 10:01:01 [OK]   started successfully

Options

--cmd    Launch command (single task mode)
--match  Substring to match against process cmdline
--log    Log file path (default: watchdog.log next to script)

Requirements

• Python 3.6+
• No pip installs needed